This invention relates generally to a system and method for depositing a target material on a substrate and in particular to a system and method for depositing a target material having a radial profile onto a substrate.
It is desirable to place radial thickness or composition profiles and/or gradients of target materials onto a substrate. A radial thickness profile or gradient is an amount of material being deposited in a radial manner (to form, for example, an annular ring around the substrate) onto the substrate. The thickness of that target material can be varied along the radius of the substrate to form the radial thickness gradients or other profiles of material. In prior systems, a particular portion of material is deposited onto a first portion of the substrate. Then, the substrate may be rotated to a second position and another particular portion of material is deposited onto the substrate with the substrate in the second position. Then the substrate may be rotated to a third position and the same process is repeated. In this manner, thickness gradients may be generated, but the gradients or other profiles are oriented with respect to specific directions on the substrate, such as along the legs of a triangle for a ternary system. Xiang, xe2x80x9cCombinatorial Materials Synthesis and Screening: An Integrated Materials Chip Approach to Discovery and Optimization of Functional Materialsxe2x80x9d, Ann. Rev. Mater. Sci. 1999, pgs. 149-171 (1999).
Thus, it is desirable to provide a method and apparatus for creating radial thickness or composition gradients or other radial symmetric profiles on a substrate that eliminates the above limitations with the conventional system and it is to this end that the present invention is directed.
The method and apparatus in accordance with the invention permits a radial thickness and/or composition gradient or other radial profile (including symmetric and asymmetric profiles) on a substrate to be formed wherein the gradients or profiles are not oriented in specific directions as is done with the prior systems. To accomplish the above, the system comprises one or more dynamic shutters (e.g., shutters that can be moved independently of each other and during the deposition of a material) in combination with equipment that permits rotation of the substrate relative to the shutter(s), or rotation of the shutter(s) relative to the substrate, during the deposition of the material onto the substrate. The equipment may also stop/start, continuously rotate at a constant speed or rotate the substrate at a variable speed during the deposition of the material to generate various different radial thickness or composition gradients or other arbitrary but radial profiles on the substrate (including symmetric and asymmetric profiles.) The system may also include one or more contact masks that may be placed on the substrate during the deposition in order to mask off particular portions of the substrate during the deposition process. The system may also include one or more deposition sources to perform deposition of substances. With multiple deposition sources, each source and shutter generates its own independent radial gradient or other arbitrary radial profile, such as a symmetric or asymmetric profiles. For convenience, the system is described in the context of rotation of the substrate, relative to non-rotating shutters. However, one skilled in the art will recognize that an equivalent system could be implemented, in which the substrate is fixed, and the dynamic shutter(s) are rotated around the substrate (as well as moved according to their other capabilities as described herein).
In accordance with the invention, the system causes a rotation of the substrate relative to the shutter(s) (e.g., the substrate is rotated and the shutter(s) are stationary or the shutter(s) rotate and the substrate is stationary) during deposition in order to induce a radial component into the thickness composition profile or composition gradient. For example, the substrate may be rotated sufficiently quickly, relative to the deposition rate, to create thickness profiles that are conical (e.g., low at the edges and higher in the middle of the substrate), reverse conical (e.g., low at the middle of the substrate and high at the edges of the substrate), concave, convex or any other radial profiles. The radial deposited component may be symmetric or asymmetric.
The parameters of the system in accordance with the invention may be varied in order to change the profiles being generated by the system. For example, the shutter shapes, the shutter positions, the shutter motion profiles, the substrate rotation speed and the substrate rotation centricity (whether or not the substrate is rotated about its center) can all be independently controlled and adjusted to generate various profiles, such as continuous gradients of discrete compositional regions or other desired film thickness profiles across the substrate.
In accordance with the invention, an apparatus for creating a radial profile of a target material on a substrate is provided. The apparatus comprises a deposition source for directing a target material toward a substrate and a shutter that blocks an amount of the target material from striking the substrate. The apparatus further comprises a rotatable platform that induces rotation of the substrate relative to the shutter system during the deposition of the target material and the shutter blocks a predetermined amount of the target material to generate a radial profile.
In accordance with another aspect of the invention, a method for deposition of a radial profile of a target material onto a substrate is provided. The method comprises directing target material toward a substrate, blocking some predetermined portion of the target material so that it does not strike the substrate, and rotating the substrate while the target material is directed toward the substrate so that a radial profile is formed on the substrate. In accordance with yet another aspect of the invention, a substrate comprises a target material formed on top of the substrate, the target material having a radial profile wherein the radial profile of the target material on the substrate is formed using at least one shutter that blocks a predetermined amount of target material while the substrate is being rotated.